Conventional circuit switched telecommunication networks set up a connection between two subscribers along a path which may include one or more switches and a variety of network transmission elements such as a trunked wireline telephone system, an optical fiber link, a microwave link, a mobile phone (wireless) link, a cordless telephone link, etc. There is a demand for distributed private networks which may interface with public telecommunications networks. The private networks may be part of an Integrated Services Digital Network (ISDN). Signaling protocols for private networks are often referred to the "Q" reference point or interface, e.g. between two Integrated Service Private Branch Exchanges (ISPBX) or Private Telecommunication Network Exchanges (PTNX). The "Q" reference point is defined, for instance, in the standards ENV 41004 or ISO/IEC 11579-1. Whereas public networks deal with subscribers on a hierarchical network-subscriber basis using network-subscriber protocols and a centralized organization for maintaining uniformity throughout the network, private networks generally include peer-to-peer protocols, i.e. the network includes nodes all of which have more or less then same ranking within the network hierarchy. Services provided within telecommunications networks may be described as either basic or supplementary. Basic services are defined for instance, in CCITT Rec. 1.210 and relate to the provision of methods of transferring information, e.g. establishing maintaining and clearing speech, data, facsimile or teleservices. Supplementary services (defined for instance in CCITT Rec. 1.210) are termed supplementary because they have no independent existence but require a basic service which they can supplement. An example of a supplementary service is call-forwarding which, without the basic service of a speech call, has no meaning. Whereas basic services are relatively static, are well documented and standardized, the supplementary services are more subject to change and are less well standardized. For this reason there exist several semi-proprietary supplementary services standards. This creates a potential problem when supplementary services are requested across standards boundaries--it is probable that request formulated in accordance with one standard will not be understood in the other system and so the supplementary service fails.
Messages which are passed through a peer-to-peer system from a first node to a receiving node, must contain sufficient information for a required operation to be completed successfully at the receiving node. Messages are generally controlled by some type of messaging protocol which determines the format of the signals passed across the network. Signaling messages are used for control of each call and of the network and may be broken up into information elements, each information element having a specific format. An example of an information element is a FACILITY information element. Operations are specified in messages by an operation code for identifying the operation. There are various standards for the format of these operation codes. For instance, for supplementary services, some operation code formats in the Abstract Syntax Notation number 1 (ASN-1) form are shown in FIG. 1 for the ECMA164 (Private Telecommunications Network (PTN) signaling between telephone exchanges--protocol for the support of name identification--supplementary services) and the ISO/IEC 13868 (Information Technology--telecommunications and information exchange between systems--private integrated services network inter-exchange signaling protocol--name identification supplementary services) standards. The operation identifier in accordance with ECMA-164 may be called "Object Identifier" (OI) and in accordance with ISO/IEC 13868 "Integer Value" (IV). In accordance with OI the operation is specified in terms of an Object identifier which is followed by the operation argument. On the other hand for IV, there is no object identifier, instead an integer value is used to identify the operation and this value is followed by the operation argument.
A node in the system which is configured to accept OI does not normally recognize IV and vice-versa, even when the operation and argument are identical. The result may depend upon the system involved, e.g. operation discarded, operation rejected, call cleared, but finally the important point is that the supplementary service does not function as expected.
With reference to FIG. 2, a terminal device of user 1 is connected to a node 3 of the private network, e.g. a switch, and a terminal device of user 2 is connected to node 4. The terminal devices may be telephones, personal computers, modems etc. Nodes 3 and 4 may be connected through another network 5 which may be a public or private telephone network. The public telephone network 5 may use another signaling protocol, e.g. the common channel signaling system 7 (SS7). Assuming that node 4 uses OI for reception and transmission, node 3 and node 4 cannot carry out supplementary services correctly if node 3 uses IV for reception and transmission. Even if the network 5 can carry the operation identifiers from nodes 3 and 4, the network 5 does not translate the operation identifier into that required for the respective receiving network 4, 3.
One known method of solving this problem is to provide at least some of the nodes of the private network with so-called "Remote Capability" known from the "MERIDIAN 1" range of products supplied by NORTEL (Northern Telecom) Ltd. of Canada. A node with remote capability can receive either the IV or OI conventions and transmit the convention indicated for the next node in accordance with remote capability. Hence, if node 3 is provided with remote capability, it uses either OI or IV conventions depending upon the operation identifier convention of the nearest remote node connected on the link. For node 3, the operation identifier convention (OIC) supported at reception is placed in the middle of the circle, i.e. SSI: OI and IV. The OIC used for transmission is given above the arrow pointing towards the next node 4, i.e. SSI: OI. By providing strategically placed nodes throughout the network having the remote capability, many of the problems with heterogeneous operation identifiers can be solved.
However, as the private network becomes more complex, remote capability switches only provide a solution if almost every switch has this capability. As shown in FIG. 3, user terminal devices 10, 20, 30 and 40 are connected to nodes 11, 21, 31, and 41 respectively. Nodes 11 and 21 are provided with remote capability. For a first supplementary service (SS1) node 11 uses OI and for a second supplementary service (SS2) node 11 use IV when transmitting towards node 21 (two arrows towards node 21). When sending to node 11, node 21 uses the same conventions (SS1:OI and SS2:IV Nodes 11 and 21 can receive both OI and IV operator identifiers (SS1:OI-IV, and SS2:OI-IV within the circles of nodes 11 and 21). Nodes 31 and 41 do not have remote capability. Node 31 uses OI for both transmit and receive for both supplementary services, whereas node 41 uses OI for reception and transmission of supplementary service 1 (SS1:OI within the circle of node 41 in FIG. 3) and IV for transmission and reception of supplementary service 2 (SS2:IV within the circle of node 41 in FIG. 3). When communicating with nodes 31 and 41, node 21 uses the appropriate operation identifier as determined by its remote capability function, i.e. for (SS1 and SS2 towards node 31 node 21 uses OI, for SS1 and SS2 towards node 41, node 21 uses OI and IV respectively.
A call between user 10 and 20 is handled by nodes 11 and 21. As both nodes have remote capability there is no problem.
A call between user 10 and 40 involving SS1 is also successful. Node 11 uses OI for (SS1 in the direction of node 21. Node 21 passes this on in a transparent way to node 41 which expects OI for (SS1. Similarly, for SS2, node 11 sends with IV. This is passed on transparently by node 21 to node 41 which expects IV.
For calls between user 10 and 30, the results are only partly successful. For (SS1, node 11 uses OI which is passed on transparently by node 21 and which node 31 expects. However, for SS2, node 11 uses IV which is not expected by node 31. Hence, the supplementary service 2 will fail. This problem can be solved by changing the operation identifier at node 31. This may be difficult if it is an old switch and the necessary soft-ware up-dates are not available. Further, changing node 31 may only push the problem one node further down the line in the network served by node 31. Alternatively, node 31 may be replaced with a switch with remote capability and old node 31 discarded or re-used somewhere else in the system. If node 31 is a vital node, there may be operational restrictions which prevent the node being replaced. Further, there is no guarantee that the old node 31 can be re-used somewhere else in the system.
It is an object of the present invention to provide a network and a method of operating the same which allows nodes configured for heterogeneous information elements, particularly operation identifiers.
It is an object of the present invention to provide equipment which allows expansion of existing peer-to-peer networks using equipment capable of dealing with heterogeneous information elements, particularly operation identifiers.